The inventive concept relates generally to semiconductor memory devices, and more particularly, controllers for multi-level memory devices and error correcting methods.
Semiconductor memory devices are a vital microelectronic component commonly found in digital logic systems, such as computers, and microprocessor-based applications ranging from satellites to consumer electronics. Thus, advances in the fabrication of semiconductor memory devices, including process enhancements and circuit-design-related developments that allow scaling to higher memory densities and faster operating speeds, improve performance standards across a broad range of products.
Semiconductor memory devices generally include volatile memory devices, such as random access memory (RAM) devices, and nonvolatile memory devices. In RAM devices, data is stored by either establishing the logic state of a bistable flip-flop such as in a static random access memory (SRAM), or by charging/discharging a capacitor in a dynamic random access memory (DRAM). In both SRAM and DRAM devices, data remains stored only so long as power is applied.
Mask Read-Only Memory (MROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), and Electrically Erasable Programmable Read-Only Memory (EEPROM) devices are examples of nonvolatile memory devices that are capable of retaining stored data in the absence of applied power. Nonvolatile memory devices may store data on a be permanent or reprogrammable basis depending on the fabrication technology used to implement the constituent memory cells and access circuitry. Nonvolatile semiconductor memories are used to store program and microcode storage in a wide variety of applications in the computer, avionics, telecommunications, and consumer electronics industries. Single-chip combinations of volatile and nonvolatile memory storage modes are available in devices such as nonvolatile SRAM (nvRAM) for use in systems that require fast, reprogrammable nonvolatile memory. In addition, dozens of special memory architectures have evolved which contain some additional logic circuitry to optimize their performance for application-specific tasks.
Mask Read-Only Memory (MROM), Programmable Read-Only Memory (PROM) and Erasable Programmable Read-Only Memory (EPROM) are not readily reprogrammable and require the application of external devices to erase and/or write new data. In contrast, Electrically Erasable Programmable Read-Only Memory (EEPROM) nonvolatile memory devices are electrically erasable and writable, and may, thus, be readily applied to auxiliary memories or system programming memories that require continuous update.